Campaign Viral Chart: Hollywood boosts shares of top viral ads

An ad starring Hollywood actor Samuel L Jackson, paid for by the Jewish Council for Education and Research in support of Barack Obama, has been shared 492,006 times in the past seven days making it the most shared ad this week.

The ad is written by Adam Mansbach, the author of 'Go the F*ck to Sleep', a comedic take on the childrens' storybook format read by Jackson, which was also a viral hit.

Meanwhile, an official ad for the Obama campaign comes third, trailled by an ad for Republican rival Mitt Romney in fourth.

Robin Williams, Betty White and a cast of famous actors and performers star in an ad for St Jude's Research Hospital, in fifth place.

The ad, created in-house, starts with ill children singing along to the Beatle's classic 'Hey Jude' and progresses to include hospital staff and celebrities, and has been shared 51,799 times.